Printing mechanisms fire drops of printing fluid (e.g., ink) onto a print medium (e.g., paper) to generate an image. These mechanisms may be used in a wide variety of applications, including computer printers, plotters, copiers, facsimile machines, and so forth. A printing apparatus may include a print head having a plurality of independently addressable firing units. Each firing unit may include a fluid chamber connected to a fluid source and to a fluid outlet nozzle. A transducer within the fluid chamber provides the energy for firing fluid drops from the nozzles. In some printers, the transducers are thin-film resistors that generate sufficient heat during application of a voltage pulse to vaporize a quantity of printing fluid. This vaporization is sufficient to fire a fluid drop out of the nozzle and onto the print medium.